1. Field of the Invention
The invention generally relates to a carrier head utilized during chemical mechanical polishing of substrates.
2. Description of the Related Art
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer. If the outer surface of the substrate is non-planar, then a photoresist layer placed thereon is also non-planar. A photoresist layer is typically patterned by a photolithographic apparatus that focuses a light image onto the photoresist. If the outer surface of the substrate is sufficiently non-planar, then the maximum height difference between the peaks and valleys of the outer surface may exceed the depth of focus of the imaging apparatus, and it will be impossible to properly focus the light image onto the outer substrate surface. Therefore, there is a need to periodically planarize the substrate surface to provide a substantially planar layer surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted to a carrier or polishing head. The exposed surface of the substrate is then placed against a rotating polishing pad. The carrier provides a controllable load, i.e., pressure, on the substrate to press it against the polishing pad. In addition, the carrier may rotate to provide additional motion between the substrate and polishing pad. A polishing slurry, including an abrasive and at least one chemically-reactive agent, may be distributed over the polishing pad to provide an abrasive chemical solution at the interface between the pad and substrate.
Typically, the carrier head is used to remove the substrate from the polishing pad after the polishing process has been completed. The substrate is vacuum-chucked to the underside of the carrier head. When the carrier head is retracted, the substrate is lifted off the polishing pad.
One problem that has been encountered in CMP is that during the course of polishing the wafer, vibrations of both high and low frequencies are produced, causing various problems associated with manufacturing efficiency and incremental increase in operating costs. High frequency vibrations ( greater than 250 Hz and  less than 20 kHz) produced during polishing may present environmental, health and safety issues, while low frequency vibrations ( less than 250 Hz) produced during polishing present may present reliability issues. For instance, the vibrations produced may cause gimbal screws to loosen, leading to slipped wafers. In addition, the polishing induced energy transmitted between the components in the carrier head may create resonance and amplification response that produce an inordinate amount of sound. The polishing induced energy may further cause relative bending movement within the polishing system.
A consideration in solving the problems associated with vibrations is developing a solution that is both cost efficient and ergonomically plausible, while still adhering to the established regulatory standards of the workplace.
Accordingly, a need exists for a chemical mechanical polishing apparatus that optimizes polishing throughput while minimizing vibrations during the course of polishing the wafer.
Embodiments of the present invention are generally directed to a carrier head for positioning a substrate on a polishing surface. In one embodiment, the carrier head includes: a housing connectable to a drive shaft to rotate therewith; a base; a detachable plate removably mounted on top of the housing; a gimbal mechanism connecting the housing to the base to permit the base to move with respect to the housing such that the base remains substantially parallel to the polishing surface; and a flexible membrane defining a mounting surface for the substrate.
Another embodiment of the present invention is directed to a carrier head for positioning a substrate on a polishing surface. The carrier head includes: a housing connectable to a drive shaft to rotate therewith; a base; a gimbal mechanism connecting the housing to the base to permit the base to move with respect to the housing such that the base remains substantially parallel to the polishing surface. The gimbal mechanism includes: a rod slidably disposed in a vertical passage in the housing; and a ring integrally connected to the rod. The ring defines a lower ring portion and an upper ring portion. The upper ring portion is made of a lighter material than the lower ring portion. The carrier head further includes a flexible membrane defining a mounting surface for the substrate.
Another embodiment of the present invention is directed to a carrier head for a chemical mechanical polishing apparatus. The apparatus includes: a housing connectable to a drive shaft to rotate therewith; a loading mechanism connecting the housing to a base to permit vertical movement of the base relative to the housing; and a detachable plate removably mounted on the housing.
Yet another embodiment of the present invention is directed to carrier head for a chemical mechanical polishing apparatus. The apparatus includes: a housing connectable to a drive shaft to rotate therewith; a loading mechanism connecting the housing to a base to permit vertical movement of the base relative to the housing; and a gimbal mechanism connecting the housing to the base to permit the base to move with respect to the housing such that the base remains substantially parallel to a polishing surface associated with the chemical mechanical polishing apparatus. The gimbal mechanism includes a dampening ring configured to dampen vibrations generated while polishing the substrate.